The process of hair care is multifaceted and generally involves washing, conditioning, and styling the hair. The desirable results of the hair care process include a persistent look and feel of clean hair between washings, ease of combing, absence of static electricity, manageability, soft feel and shine. A limited number of hair care products are available which clean as well as condition the hair by the use of one product, i.e., a two-in-one conditioning shampoo. Certain two-in-one conditioning shampoos typically contain water, anionic surfactants, foam stabilizers, insoluble nonvolatile silicone conditioning agents and silicone suspending agents. Other such products contain cationic conditioning agents in place of silicone. However, all of these singular shampoo products and/or two-in-one products have various limitations. These limitations are well known in the art. Other hair care products are available which simultaneously clean, condition and control dandruff, i.e., a 3-in-1 anti-dandruff shampoo. These too have well known limitations.
Since known two- and three-in-one hair care products have various limitations, a need exists for surfactant based shampoo compositions which are capable of delivering cleaning, foaming and/or conditioning properties to the hair, with limited or no build up of the compositions on the hair after multiple application. It is desired that new hair care compositions provide comparable or superior cleaning, foaming and/or conditioning properties to the hair, as compared to prior art hair care compositions. Further, a need exists for compositions with the above-described properties which are efficacious on fine, long, or chemically damaged hair.
General detergent anionic-cationic surfactant mixtures are well known to the art. See generally, U.S. Pat. Nos. 5,441,541, 5,472,455, 5,204,010, 4,790,856, 4,298,480, 3,730,912 (all to The Colgate-Palmolive Company), 5,622,925, 5,607,980, 5,565,145, 4,913,828, 4,659,802, 4,436,653, 4,338,204, 4,333,862, 4,132,680 (all to The Procter & Gamble Co.); also see WO 97/03164, WO 97/12022 and WO 96/37591 (all to The Procter & Gamble Co.), and WO 97/28238 and WO 97/15647 (both to Reckitt & Colman, Inc.). See also, U.S. Pat. Nos. 5,610,187 and 4,247,538 (both to Witco Corp.), 5,344,949 (to Th. Goldschmidt AG), 5,332,854 and 5,324,862 (both to Dai-Ichi Kogoyo Seiyaku Co., Ltd.), 4,273,760 (to National Starch and Chemical), and 4,264,457 (to DeSoto, Inc.). Mixed surfactant systems have also been disclosed in "Mixed Surfactant Systems", ACS Symposium Series 501, P. M. Holland and D. N. Rubingh (Jun. 17-19, 1991).
Additionally, there have been many studies and symposia on mixed surfactant systems. See, for example, Scamehorn, J. F., ed., "Phenomena in Mixed Surfactant Systems", ACS Symposium Series 311, Washington, D.C. (1986). The effects of alkyl groups and oxyethylene groups in nonionic surfactants on the surface tension of anionic-nonionic systems have been described. See Abe et al., J. Colloid Interface Sci., 107, p. 503 (1985); Ogino et al., J. Colloid Interface Sci., 107, p. 509 (1985); and Rosen et al., J. Colloid Interface Sci., 95, 443 (1983). Interaction between betaines and cationic surfactants has also been studied. See Zhu et al., J. Colloid Interface Sci., 108, 423 (1985).
Mixed surfactant systems have shown synergistic improvements in surfactant properties compared to the properties of their individual surfactant components. Synergism increases with the degree of charge difference. Thus, the greatest synergistic surfactant property improvements are realized when mixing anionic and cationic surfactants. See Rosen et al. in "Phenomena in Mixed Surfactant Systems" (Scamehorn, J. F., ed.), ACS Symposium Series 311, Washington, D.C. (1986), pp. 144-162; Zhao et al. in "Phenomena in Mixed Surfactant Systems" (Scamehorn, J. F., ed.) ACS Symposium Series 311, Washington, D.C. (1986) pp. 184-198.
In detergent applications, although in principle any surfactant is suitable, in practice only anionic and nonionic surfactants typically are used. Cationic surfactants, especially quaternary ammonium salts, can decrease detergency and enhance soil redeposition when used in heavy-duty liquid detergents. Consequently, there is a general notion that anionic and cationic surfactants cannot be used in the same formula without loss of efficacy. Similar worries regarding potential loss of efficacy exist when contemplating use of cationic surfactants in hair and skin conditioning applications. Thus, anionic-cationic surfactant mixtures have been used only sparingly in the production of consumer cleaning products and personal care products.
Studies on anionic-cationic systems are recent and few compared to studies on other mixed surfactant systems. However, strong synergism has been exhibited by these systems. Surface activity properties, particularly the critical micelle concentration (cmc), surface tension, and microemulsion behavior (Bourrel et al., Tenside Detergents, 21, 311 (1984)), were the most studied properties. For example, the surface activities of mixed aqueous solutions of sodium dihexylsulfosuccinate with dioctyl(hydroxyethyl)methylammonium chloride and sodium dihexylsulfosuccinate with octyl(hydroxyethyl)dimethylammonium chloride were much higher than those of the single surfactants. See Zao, G., Huoxue Xuebo, 43, 705 (1985) (Ch. Chem. Abstracts 103:184033n). The strong synergistic effect on surface pressure for mixed solutions of cationic and anionic surfactants has been studied quantitatively. When dilute solutions of sodium dodecylsulfate and dodecyltrimethylammonium bromide were mixed, tile surface pressure increased by more than 40 mN/m. Also, the cmc and the minimum surface tension were lower for the mixture than for either the anionic or cationic surfactants alone (Lucassen-Reynders et al., J. Colloid Interface Sci., 81, p. 150 (1981)).
However, mixed anionic-cationic mixtures also have shown antagonistic effects relative to the properties of the individual surfactant components. See Chobanu et al., Izv. Akad. Nauk. Mold. SSR, Ser. Biol. Khim. Nauk., 5, p. 66 (1982). Unlike other mixed surfactant systems, most anionic-cationic surfactant mixtures studied are insoluble or only slightly soluble in water. Hence, practical use of anionic-cationic surfactant mixtures has been very limited in areas where a relatively high concentration of surfactants is needed (see U.S. Pat. No. 5,472,455, to Mehreteab, issued Dec. 5, 1995). Thus, there is a need for soluble anionic-cationic surfactant mixtures.
At present, very few anionic-cationic surfactant mixtures have been found which produce clear solution phases over a wide concentration range at equimolar composition. See generally, Khan, A.; Marques, E.; Spec. Surfactants 1997, 37-80, edited by Robb, I. D. Blackie. Typically, anionic-cationic surfactant mixtures are present as microemulsions, rather than as clear, homogeneous solutions. Usually, the anionic and/or cationic surfactant must be alkoxylated to even maintain such a microemulsion.
Because the probability of synergism between surfactants increases with the strength of interaction, the greatest probability of synergism with anionic surfactants exists in anionic-cationic or anionic-zwiterionic mixtures. See generally, Surfactant and Interfacial Phenomena; Rosen, M.; John Wiley & Sons, Inc. 1989 p. 402. Surfactant performance is gauged by the so-called .beta. value, which is a negative number indicating how much less a system's actual surface tension is compared to its calculated surface tension. Surfactant mixtures exhibiting larger deviations between calculated and actual surface tension perform better; thus, surfactant performance increases with progressively more negative .beta. values. However, with respect to anionic-cationic mixtures, the variations in surfactant type and size that produce progressively more negative .beta. values unfortunately are accompanied by decreasing solubility. Hence anionic-cationic synergism is limited by the formation of an insoluble salt, which typically occurs when the combined number of carbon atoms in the chains of both surfactants totals more than about twenty. See generally, Lomax, E; Specialty Chemicals 1993, v 13 n 4 p 223-227). A method for enhancing the solubility of anionic-cationic surfactant mixtures is therefore needed to allow achieving maximum negative .beta. values.
In addition to detergent mixed surfactant systems, shampoo compositions comprising anionic-cationic surfactant mixtures are also relatively well known. U.S. Pat. No. 6,007,802 (to Procter & Gamble) discloses a conditioning shampoo composition with excellent cleaning performance and improved levels of conditioning while minimizing any adverse effect associated with build-up; the disclosed compositions general comprise an ethoxylated alkyl sulfate, amphoteric surfactant, insoluble, dispersed conditioning agent (nonionic, cationic silicone), synthetic esters, and cellulosic cationic polymers. U.S. Pat. No. 5,939,059 (to Akzo Nobel) discloses a 2-in-1 conditioning shampoo comprising an anionic surfactant (alkyl sulfate or ether sulfate) and ester quats, with optional amide. U.S. Pat. No. 5,747,436 (to Colgate Palmolive) discloses a low static conditioning shampoo comprising an anionic and an amphoteric surfactant, complex acid:amine (1:1 mole ratio) and polyquaternary compound. U.S. Pat. No. 5,607,980 (to Procter & Gamble) discloses topical compositions having improved skin feel comprising an anionic surfactant (alkyl sulfate, ether sulfate, isethionate), a cationic surfactant and an amphoteric surfactant. U.S. Pat. No. 5,997,854 (to Henkel) discloses a conditioning shampoo formulation comprising a quaternary ammonium component, an emulsifier, an amphoteric, an alkyl polyglycoside surfactant. U.S. Pat. No. 5,145,607 (to Takasago International Corporation) discloses an optically clear conditioning shampoo comprising anionic (alkyl sulfate or alkyl ether sulfate) and cationic surfactants. U.S. Pat. No. 4,931,216 (to Kao Corporation) discloses detergent compositions comprising an anionic or amphoteric surface active agents and a branched quaternary ammonium salt. U.S. Pat. No. 4,744,977 (to Henkel) discloses quaternary ammonium compound hair conditioners in combination with an anionic surfactant. U.S. Pat. No. 5,661,189 (to Unilever) discloses mixtures of anionic, cationic, amphoteric, nonionic, zwitterionic surfactants, along with benefit agents, thickening agents an small amounts of soap.
Additionally, WO 98/29094 (to Procter & Gamble) discloses conditioning shampoo compositions comprising a polyhydrophilic anionic surfactant, a cationic surfactant, and a polyvalent cation, along with optional amphoteric surfactants. EP0937452A2 (to Goldwell) discloses hair conditioning agents containing esterquats and anionic compounds. JP-62126113 (to Lion) discloses shampoos containing quaternary ammonium salts and anionic surfactants, such as alkyl sulfate, ether sulfate and olefin sulfonate. JP-63156713 (to Kokai Tokkyo Koko) discloses shampoos containing cationic surfactants, amphoteric sulfonates, alpha olefin sulfonates and various other sulfates. JP-6293620 (to Kokai Tokkyo Koko) discloses shampoos compositions containing anionic (ether sulfate, sulfosuccinate), amphoteric and cationic surfactants. JP-63313711 (to Kokai Tokkyo Koko) discloses shampoo compositions containing alpha olefin sulfonates and/or sulfate salts, quaternary ammonium salts and amidoalkyl betaine surfactants.
For other mixed surfactant systems for use in shampoo formulations, see generally, U.S. Pat. Nos. 4,913,828 (to Procter & Gamble); 5,441,541 (to Colgate-Palmolive); 4,978,526 (to Inolex); 3,929,678 (to Procter & Gamble); and 5,622,925 (to Colgate-Palmolive). Additionally, see WO 99/58106 (to Witco); JP 2558704 (to Lion); WO 97/12022 (to Procter & Gamble); and WO 97/03164 (to Procter & Gamble).
Generally and without being bound by any particular theory, the general benefits associated with solubilized anionic/cationic systems are best explained by the theory that surfactant molecules of opposite charge pack more closely to each other in micelles due to the absence of any electrostatic repulsion. This close packing in turn leads to more efficient soil removal. See generally, Lomax, E., supra. Prior art attempts to solubilize anionic-cationic surfactant systems include the use of organic solvents, such as butanol or ethanol. Also, reported is the use of nonionic surfactants as solubilizing agents or incorporation of alkoxy groups into the anionic and/or cationic surfactants. Unfortunately, addition of organic solvents presents a fire hazard and/or possible skin sensitization and is generally unacceptable in shampoo compositions. Additionally, addition of nonionic components tends to keep the anionic and cationic surfactant molecules further apart, decreasing the overall efficacy of the system. Once again without being bound by any particular theory, the oppositely charged surfactant molecules are kept further apart due to stearic hindrance and because of the osmotic effects which force water molecules between the two surfactant molecules, diminishing the beneficial effect of closer packing.
Thus, in addition to the previous mentioned needs, there is a need for anionic-cationic surfactant blends that are efficacious in shampoo formulations, readily soluble in water at a variety of concentrations, easy to handle, and safe to handle. Accordingly, it has been surprisingly discovered that soluble and substantially soluble shampoo compositions comprising mixtures of anionic and cationic surfactants can be prepared without the use of flammable organic solvents. The shampoo compositions of the present invention are anionic-cationic-bridging surfactant blends which generally form clear solutions at a variety of concentrations in water.